Wrought railroad wheels made of alloy steels



. steel at the tread surface may occur.

WRfiUGl-IT RAHLROAD WHEELS MADE OF ALLGY STEELS John M. Hodge and.lnseph M. Wandrisco, Pittsburgh,

Pa., assignors to UnitedStates Steel Corporation, a corporation of NewJersey No Drawing. Application September 3, 1954, Serial No. 454,206

2 Claims. (Cl. 75-123) The present invention relates to alloy steelwrought railroad-car Wheels.

The wrought-steel wheels used currently in railroad service aremanufactured by rolling and/or by forging plain carbon steel. Becauserailroad wheels serve as brake drums as well as means of locomotion, thetread surface of the wheel is heated by friction when the brakes areapplied. Therefore, large thermal gradients develop in the wheel duringbraking, so that the steel at the tread surface may be heated above itstransformation temperature. On cooling, the steel that was heated abovethis temperature usually undergoes a transformation to a microstructureof higher hardness and lower ductility than the hardness and theductility of the original micro structure.

This transformation results in an expansion which opposes the normalcontraction of the cooling metal and tends to set up high stresses inthe heat-affected portion of the rim. These stresses may be augmented bya further contraction which occurs when the wheel is reheated byrepetition of the braking, and the hard microstructure is tempered. Thesharp thermal gradient created by the brake heating tends to intensifythese stresses resulting from transformation and tempering. Thesestresses may be high enough to cause cracking in the heat affectedportion of the rim of the wheel, and such cracking, which is of commonoccurrence in plain carbon wheels, is known as thermal checking. Sincethe magnitude of the expansion and contraction from transformation andtempering is a function of carbon content, the susceptibility to thermalchecking is, likewise, dependent upon the carbon content. This effect ofcarbon content on susceptibility to thermal checking has been longrecognized in the trade and it is common practice to use lower carbonwheels for applications involving severe braking. In

plain carbon wheels, however, it is impractical to use carbon contentsbelow about 0.50%, as the wheels then become too soft to satisfactorilyresist wear and shelling from the rolling loads.

Because the thermal expansion of the heated steel at the tread surfaceis restrained by the unheated steel in the other parts of the wheel,plastic deformation of the On cooling, circumferential tensile stressesdevelop in the steel that has been plastically deformed and thesestresses increase in magnitude with repeated heating and cooling cycles.These stresses may be of such magnitude as to result in deep cracks inthe rim, known as thermal cracks, and on further repeated braking thesethermal cracks may propagate into, or in some instances through, theplate res Patent fiice 2,798,805 Patented July 9, 1957 of the wheel,resulting in the serious type of wheel failure, known as explosivefailure. Since the magnitude of this tensile stress depends upon theextent of the plastic deformation of the heated portion of the rim, thesusceptibility to this type of failure can be decreased by using steelsof higher elevated temperature strength which will resist thisdeformation at the elevated temperature.

The third requirement for a wheel which will perform satisfactorily inservice is a high enough strength or hardness in the tread and rim toresist wear, or fatigue failure of the tread from stresses imposed byheavy rolling loads or flow which leads to the type of fatigue failureof the treads known as shelling. This need is generally recognized andit is common practice with plain carbon wheels to use higher carbon,harder wheels for service involving heavy loading and consequently agreater tend ency to shelling.

Still another requirement for a wheel which will perform satisfactorilyin service is a sufficiently high strength level in the plate portion ofthe wheel to resist fatigue failure in this portion of the wheel.

It is accordingly an object of this invention to provide wrought steelrailway wheels which have much lower carbon content than is possible inplain carbon steel wheels without sacrifice of resistance to wear orshelling and with an attendant gain of a much lower susceptibility tothermal checking or cracking.

Another object of this invention, is the provision of a restricted rangeof carbon content, within which the occurrence of thermal checking isinsignificant even under the most severe braking conditions.

A further object of this invention is to provide wrought steel railwaywheels having enhanced elevated temperature strength.

Still another object of our invention is: the use of a steel ofsufiicient hardenability to permit the attainment of the requisitehardness and strength in the rim portion to minimize shelling and wearto permit the attainment of the desired hardness throughout the balanceof the wheel.

We have discovered that the foregoing objects can be accomplished bymaintaining the alloying contents within certain restricted ranges ashereinafter described. The first essential feature of the steel of thisinvention is the establishment of a restricted low range of carboncontent, below 0.50%, in order to insure adequate resistance to thermalchecking. This range is 0.10 to 0.30% carbon with a preferred range of0.12 to 0.24%.

The second essential feature is the use of alloying elements conduciveto elevated temperature strength and we prefer to use molybdenum andvanadium for this purpose. The ranges of these elements which may beincluded in steels of this invention are 0.10 to 1.50% molybdenum and0.01 to 0.50% vanadium and preferably .30 to .75 molybdenum and .01 to.15% vanadium. Other elements such as columbium, titanium, tungsten andcobalt could be used to partially at least replace the foregoing.

The third essential feature is the use of alloying elements conducive tohardenability. We prefer to use the alloying elements nickel, manganese,chromium and boron for this purpose. The ranges of these elements whichmay be required to obtain adequate hardenability precipitation of afinely divided alloy carbide duing cool ing from the austenitizingtemperature and on tempering. This is particularly beneficial inobtaining an adequate strength level in the plate portion of the wheelto resist fatigue failure.

Thus, the composition range of the steel of this invention is asfollows:

Range,

Preferred Percent Range Balance iron and other elements in residualamounts.

Testing machines, originally designed for the testing of brake shoes,are used to study the effect of simulated conditions of braking on thesusceptibility of full-scale wheels to thermal checking, to thermalcracking, and to the sudden fracture that results from the stressesdeveloped by repeated braking (see The Effect of Brake Shoe Action onThermal Cracking and on Failure of Wrought Steel Railway Car Wheels,University of Illinois Engineering Experiment Station, Bulletin SeriesNo. 387, June 1950).

The stop test, which simulates the braking conditions that exist when arapidly moving train is stopped suddenly in an emergency, is used todetermine the susceptibility of wheels to thermal checking and tothermal cracking. The drag test, which simulates the braking conditionthat exists when a train descending a long grade is slowedintermittently, is used to determine the susceptibility of wheels to thesudden, eXplosive-type failure that results from the propagation of athermal crack. To simulate a thermal crack, a radial saw-cut is made inthe rim of the Wheel before the drag test is conducted.

Braking tests, such as those described abovehave established that alloysteel wheels of the type of this invention have a resistance to thermalchecking, thermal cracking, and explosive failure far superior to thatof currentlyproduced plain carbon Wheels. The results of some of thesetests, conducted with wheel composed of steels of the following analysesare hereinafter set forth to illustrate the performance of alloy steelwheels of this invention.

I. Stop tests All stop tests were conducted from aninitial speed of 115M. P. H. and with a pressure of 20,000 pQllnds applied toeach oftwobrake shoes.

Steel Heat Treat- Test Procedure Results No. ment 50 Full Stops-100%energy absorption. Partial Stops5% energy absorption. 5 Partlal Stops-%energy Wheel did not absorption. thermal 1 Rim Tough- 5 Partial Stops%energy check or ened. absorption. thermal 5 Partial Stops% energy (Hackabsorption. 10 Partial Stops-% energy absorption. 5 Partial Stops%energy absorption. 50 Full Stops100% energy absorption. 5 PartialStops-10% energy Light thermal 2 do absorption. checking- 5 PartialStops-20% energy no thermal absorption. cracking. 5 Partial Stops-30%energy absorption. do.- 50 Full Stops100% energy Heavy thermalabsorption. checkingno thermal cracking.

II. Drag tests Each drag test was of 30-m1nute duration with the brakesapphed for 50 seconds during each minute. The test wheel was rotated ata constant speed of 45 M. P. H.

Steel Heat Treat- Depth of Brake N o. of No. ment Saw Out; Shoe DragsResults Percent Pressure 1 'Rim 'Iough- None 4, 000 20} Wheel did not.ened. 4, 000 tail. 3 do 75 4, 000 100 Do.

The following results of elevated temperature tensile tests on samplescut from wheels of this steel are illustrative of the superior elevatedtemperature strength .Which i as described above, an important factor inincreasing the resistance to thermal cracking and explosive failure:

Tempera- Yield Reducture of Strength Tensile Elon tion Steel No. Test,(0.2% 011- Strength, gation, of

F. set), p. s. i. percent Area,

p. s. 1. percent 900 67, 800 84, 800 -20. c 61. 5 1 -1, 000 64, 800 79,700 18. 0 58.0 1, 100 58, 800 69, 800 14. 0 33. 0 900 81, 000 101, 20022. 0 65. 0 3 1, 000 77, 000 90, 500 20. 0 66. 0 1, 100 58, 300 77, 40024. 0 54. 0 4 900 50, 800 80, 000 31. 0 73. 0 ;o7 carbon 1, 000 41, 00060, 400 39.0 71. 0 Plain carbon. 1, 100 25, 200 40, 600 as. 0 74. 5

The following resultsof fatigue tests on samples cut from the platesofan alloy wheel of the type of this in- .vention and a similar plaincarbon wheel will illustrate the superior resistance to plate fatiguefailureof the alloy steel wheel.

Endurance Hardness Steel No. Heat Treatment Limit, BHN

1. Rim Toughened 61, 500 223/229 5- do 49, 500 223/229 The aboveexamples are illustrative of the superior performance and properties ofalloy steel wheels of the type of this invention. As a result of ourdiscoveries, we have produced a superior wrought railway Wheel which ischaracterized by substantial freedom from thermal checking and crackingunder severe braking conditions due to its containing less than 0.50%carbon and having an elevated temperature yield strength in the rimportion in excess of 60,000 p. s. i. at 1000 F. when heat treated to ahardness in excess of 250 BHN and having a room temperature yieldstrength in the plate portion in excess of 60,000 p. s. i. when heattreated to a hardness value in excess of 220 BHN.

While we have shown and described several specific embodiments of ourinvention, it will be understood that these embodiments are merely forthe purpose of illustration and description and that various other formsmay be devised within the scope of our invention, as defined in theappended claims.

We claim:

1. A wrought steel railway wheel having an elevated temperature yieldstrength in excess of 60,000 p. s. i. at 1000 F. in the rim portion whenheat treated to a hardness in excess of 250 BHN and having a roomtemperature fatigue strength in the plate portion in excess of 60,000 p.s. i. when heat treated to a hardness value in excess of 220 BHN, saidwheel being characterized by substantial freedom from thermal checkingand cracking under severe braking conditions, the steel of said wheelcontaining with the balance iron and residual amounts of other elements.

2. A wrought steel railway wheel having an elevated temperature yieldstrength in excess of 60,000 p. s. i. at 1000 F. in the rim portion whenheat treated to a hardness in excess of 250 BHN and having a roomtemperature fatigue strength in the plate portion in excess of 60,000 p.s. i. when-heat treated to a hardness value in excess of 220 BHN, saidwheel being characterized by substantial freedom from thermal checkingand cracking under severe braking conditions, the steel of said Wheelcontaining References Cited in the file of this patent UNITED STATESPATENTS 2,586,042 Hodge et a1. Feb. 19, 1952

2. A WROUGHT STEEL RAILWAY WHEEL HAVING AN ELEVATED TEMPERATURE YIELDSTRENGTH IN EXCESS OF 60,000 P.S.I. AT 1000* F. IN THE RIM PORTION WHRNHEAT TREATED TO A HARDNESS IN EXCESS OF 250 BHN AND HAVING A ROOMTEMPERATURE FATIGUE STRENGTH IN THE PLATE PORTION IN EXCESS OF 60,000P.S.I. WHEN HEAT TREATED TO A HARDNESS VALUE IN EXCESS OF 220 BHN, SAIDWHEEL BEING CHARACTERIZED BY SUBSTANTIAL FREEDOM FROM THERMAL CHECKINGAND CRACKING UNDER SEVERE BRAKING CONDITIONS, THE STEEL OF SAID WHEELCONTAINING